Starting on 1/8/21 all 7 of my Yealink T46S phones will intermittently all lose registration. I have a ticket open with RingCentral support, and they just keep saying it isn't on their side and just keep pointing me to the network requirements documentation (https://support.ringcentral.com/article/9233.html). We have implement all of the recommendations but we are still having the issues.

Here are the details. If we happen to be on a call when the issue happens, we can hear the caller, but they can not hear us. Then after about 30 seconds, the call will drop and all the phones will go to a "No Service" "No Registration" status. During this time, we are able to browse any web pages, we can ping sip.ringcentral.com and tracert sip.ringcentral.com just fine. Then after about 3-4 mins the phones will successfully register just fine.

We have worked with our SDWAN provider and local IT consultant and we can not identify what is causing the de-registration issues. Does anyone have any suggestions?